Methods of biological control are a long-standing and potentially powerful alternative to pesticides for insect control and control of the diseases insects spread. One method currently employed for the control of insect populations is termed the “sterile insect technique” (SIT). SIT has been applied worldwide to eradicate specific populations of agricultural pests or disease vectors, including the mosquito. For the last 30 years, SIT has relied on classical genetic manipulation to generate genetic sexing strains for mass production of exclusively male insects. These males, generally sterilized by irradiation, are released into the wild in large numbers to produce ineffectual matings with wild females. As a result, there are no progeny from these wild female insects and the insect population is dramatically reduced. Irradiation of male insects, however, puts them at a competitive disadvantage with wild males.
A more desirable modification of the traditional SIT approach, called “release of insects carrying a dominant lethal” (RIDL) depends on female-specific promoter/enhancer elements to bring about female lethality by induced expression of a dominant female-specific lethal effector. In this manner, the males are not irradiated, and are reproductively competitive with wild male populations.
Female-specific expression in insects also has the potential to provide an important tool to control transmission of infectious diseases transmitted to the human population by these insects. One option is to have transgenes that will prevent pathogen transmission linked to other transgenes that confer a selective advantage to the transgenic mosquito strain in terms of reproductive fitness, pesticide and/or pathogen resistance.
A remaining challenge to these techniques, however, is the compromised reproductive fitness of the transgenic insects caused by the specific transgenes they harbor. Hence, there is a need for female-specific promoter/enhancer elements to generate female-specific expression. Ideally, the expression system would direct expression in female fat bodies at a late stage of insect larval development, as expression of transgenes in the fat body of female insects could confer greater fertility and fecundity to transgenic insects.